Hydraulic lifting and separating wedges are known. These wedges usually consist of a central wedge-shaped portion located between two external plates. The external plates are located between the objects to be separated or under the object to be lifted, and the wedge is driven forward between the two plates in order to push the plates apart, thereby separating the objects or lifting the object.
It is known to couple the plates by a pin and slot arrangement so that the or each plate moves in only one direction. A disadvantage with this is that the load of the objects being separated is concentrated at a critical point and so the plates tend to bend and the mechanism may subsequently jam.